1. Field of the Invention
The present invention relates to devices which allow control of the navigation of a towed underwater object, particularly of a towed linear acoustic antenna, more particularly to keep the latter at a constant immersion and at a constant distance from other towed linear antennas parallel to it so as to form an array in the form of a comb. These acoustic antennas are more particularly used in oil exploration.
2. Discussion of the Background
Devices of this nature are more particularly known from U.S. Pat. No. 2,744,870 filed by the applicant company on Feb. 13, 1996 under the Ser. No. 96/01741, published on Aug. 14, 1997 and granted on Mar. 6, 1998. That patent sets out in particular the operational requirements and the principle of operation of devices of this nature, which are commonly known as “birds” because of their shape and because of the presence of wings intended to generate a hydrodynamic force which acts on the cable to keep it in a determined configuration.
The birds described in that earlier patent comprise a pair of coplanar wings the inclination of which can be adjusted separately by means of two motors, thus allowing the bird to orientate itself about its axis and therefore to act on the hydrodynamic force due to the wings in direction and amplitude. The antenna or, more specifically, the segment of antenna to which the bird is fixed, can thus be made to move both in the vertical direction, as was known earlier to adjust the immersion, and in the horizontal direction to maintain the straightness of the antenna and its spacing with respect to the adjacent antennas.
However, there is no separation between the adjustment for immersion and the adjustment for lateral position. Thus, to cause the segment of antenna to move, whether only in immersion or only laterally, it is necessary to actuate both motors because the rotational positioning of the bird about the axis of the antenna is not naturally stable. The electrical power consumption under such conditions is too high for these birds to be able to be powered by a power source internal to the bird, for example batteries. Indeed, given the autonomy needed for acquiring seismic signals, the volume of batteries would be prohibitive. It is therefore necessary, as described in the abovementioned patent, to resort to the use of a transformer to transmit the power. It is therefore necessary to modify the structure of the antenna to include the transformer primary, the secondary being situated in the body of the bird, and this has the major disadvantage of preventing the use of existing antennas.